What do you think about phenomenon "egg yolk" of clinker.

Brown cores are quite commonly seen within clinker nodules when they are broken. Clinker which appears to be normal, with a dark grey colour, is found to have brown cores when the nodules are broken. This phenomena is brought about by high temperature reduction of Fe3+ to Fe2+ at the high temperatures in the burning zone. This happens after the C3S has been formed and is therefore not detrimental for strength development of cement (although colour may be affected). All clinker will be reduced to some extent by the high temperatures in the burning zone of a cement kiln. After the clinker passes under the flame the secondary air rising from the cooler re-oxidises the Fe2+ to Fe3+, but large clinker nodules may not be completely re-oxidised through to the core and remain brown in the centre. Porosity, as well as size, is a factor determining the re-oxidation of the cores, low SM clinker may be less porous, due to lower flux content, and therefore more prone to brown cores.

Thanks for the input. The egg yolk can be reduced by avoiding the reducing atmosphere in the kiln burning zone by keeping the higher kiln inlet oxygen ( around 2%)

Low SM means high amount of alumina and iron and raw mix is easy to burn.Low SM should have high flux content in contrast to your reply.Please clarify the matter.

While reduced iron can lead to the phenomenon of brown or yellow centres in clinker nodules as described above, I have come across another phenomenon that also causes something similar.

 In some brown cores at our plant I discovered that the core material tested negative to the fairly sensitive Maggotteaux test for Fe2+. This lead me to examine polished sections (imbedded in epoxy) of these nodules under a microscope.

 I found that the areas which were yellow-brown to the naked eye were physically different from the darker areas beside them in that they contained mostly closed pores, whereas the darker areas contained open pores. This lead me to believe that the colour phenomenon was related to the amount of light reflected from the clinker surface.

 Closed pores would act like small reflectors, wheareas open pores would transmit the light into depths of the nodule where it would not be able to be reflected back to the observer, rather like a fibre optic cable. Thus the area of closed pores would appear lighter (brown) and the areas of open pores would appear dark.

The Maggotteaux test seemed to confirm this hypothesis on almost every nodule I tested.

 I would suggest that to confirm whether or not the brown cores in your clinker are due to reducing conditions or this reflected light phenomenon you should perform the Maggotteaux test (reducing conditions) on the brown centers.

Regards,

Ted.

Dear Mr.Ted Krapkat, Thanks for sharing your experience regarding yellow core clinker.Such healthy discussion will raise the standard of the forum.Could you please explain briefly in the forum regarding Maggotteaux Test and instrument used for the test?All forum members will be benifited from your knowledge including myself. With regards, R.M.Sahu, India

Hello Raj,

 The Magotteaux test is a fairly simple but very sensitive test for the presence of Fe2+ in clinker, although it is qualitative rather than quantitative.

 The principle reagent used is an acidic solution of 2,2'-bipyridyl in water. Traces of Fe2+ will produce a pink colouration with the reagent, the intensity of the colour is a measure of the relative amount of Fe2+ present.

In our plant we perform this test daily. I have attached below a short method if you wish to try it out;-

 

REAGENTS:

Solution A

Weigh 0.25 g of 2,2'-bipyridyl and transfer it to a beaker.  Add 90 ml of water and 10 ml of concentrated hydrochloric acid.  Stir until the reagent has dissolved and transfer it to an amber glass bottle fitted with a dropper..

Solution B

Dissolve 50 g of tri-sodium citrate in 100 ml of water and transfer it to an amber glass  bottle fitted with a dropper.

 

APPARATUS:

A white porcelain tile, perferably with small circular depressions.

Analytical balance to weigh the reagents.

Timer. 

 

METHOD:

• Place approx. 5 to 10mg of powdered sample into a depression on the tile.
• Add 2 drops of solution A.
• If there is no pink colour after 2 minutes, add 2 drops of solution B.
• Allow to stand for a further 5 minutes. If a pink colour is now apparent then Fe2+ is present, but just above the sensitivity of the test.
• Record the result according to Table 1 below;-

Table 1: Test Results Key

Negative	Produces no discernable pink colour even after the addition of Reagent B
Very Slightly Positive	Produces no discernable pink colour with Reagent A alone and a light pink colour after the addition of Reagent B
Slightly Positive	Produces a light pink colour with Reagent A alone
Positive	Produce a pink colour with Reagent A
Strongly Positive	Produces a strong pink colour with Reagent A alone.

 

Correctly burned clinker should be nagative or very slightly positive.

The sensitivity of 2-2'-bipyridyl to Fe2+ is 1:10⁷ 

 

If you wish any further information please let me know,

 

Best regards,

 Ted. 

 

Please accept my thanks for the Magotteaux test procedure.

Dir sirs!

esp. thanks to everybody helped my question.

Best regards

HongMinh.

hello sir.

i wana know whats the procedure of check the chlorides in cement.also plz tell me due to which resion coating dropped from kiln from quality side nd from procees side.